1. Field of the Invention
The present invention is generally directed to an optical device and assembly, which provides an optical simulation of the aberrational effects of atmospheric turbulence and, more particularly, to an optical device which can be inserted into an existing optical lab collimator test facility.
2. Description of Related Art
Evaluating the effect of atmospheric turbulence on a sensor in a laboratory setting is often difficult. A typical instrumentation facility will include a set of targets located at the focal plane of a collimating optical system. The optical sensor unit being tested is normally positioned with its aperture receiving light from the target collimator. In this configuration, measurements of the sensor can be made. The simulation of atmospheric turbulence in such a system, however, would require a random variation in the focal quality of the target. Such random variation is difficult to create given that the target must be located in the focal plane of the collimator.
A number of different techniques have been used to simulate atmospheric image turbulence in laboratory settings. For example, some known systems utilize spatial light modulators (SLM) to impart a temporally varying phase. For example, U.S. Patent Appl. Pub. No. 2010/0192709 to Wilcox, et al. discloses a system including a time varying phase screen input in a liquid crystal spatial light modulator. The liquid crystal spatial light modulator receives a collimated beam from a light source such as a laser, and impresses an aberration on the wavefront of the collimated beam from the laser. The aberration that is impressed on the collimated beam by the spatial light modulator is generated by the atmospheric turbulence generator. However, such systems are limited to use in the visible wavelength regions in which liquid crystal modulators operate. Furthermore, the structure of the spatial light modulator creates a permanent wavefront deformation, which cannot be removed from the system.
Methods of approximating atmospheric turbulence are also known for use with an infrared imaging apparatus. For example, U.S. Pat. No. 5,756,990, to Watkins et al. is directed to a method for approximating effects of atmospheric turbulence on an infrared imaging apparatus. The system obtains a sampled version of an object and applies at least one spatially varying system to obtain an image intensity distribution. The spatially varying system simulates atmospheric turbulence that varies in phase and amplitude as a function of the spatial index. This system is limited to infrared imagery and is not configured for use in an optical laboratory system.
Alternatively, computer based modeling systems are used to approximate turbulence in optical systems. For example, U.S. Pat. No. 6,512,999, to Dimas et al., discloses an apparatus and method for simulating atmospheric turbulence using a computer-aided modeling system. In Dimas, turbulent flow of a fluid, relative to an object, is simulated by layering a plurality of vortex sheet layers surrounding the surfaces of a modeled object. The apparatus tracks vortex tubes growing out of an outermost layer of the plurality of vortex sheet layers, and projects the layered vortex sheets and the vortex tubes on the object.
Still other methods of simulating atmospheric turbulence require a target which is integrated into the device and projected to the tested lens. In this type of system, only the provided target can be used. The system cannot be integrated and calibrated into an existing optical laboratory system.
Many of the above-described methods cannot be used with existing optical laboratory systems. Therefore, there is a need for an optical instrument that can be easily inserted into an existing optical laboratory system, and which makes no further changes to the existing system other than providing a simulated atmospheric turbulence effect. In this way, calibration testing of non-turbulence and turbulence infused targets could be accomplished in a common system. The optical instrument of the present invention is configured to provide such beneficial results.